Multimedia services, such as voice, video and messaging services, are increasing in popularity. A core component of many Voice over Internet Protocol (VoIP) services is a telephone number mapping (ENUM) service. The ENUM service converts telephone numbers to host names. The ENUM service may be shared by multiple service providers and used in peering network agreement arrangements.
Some multimedia services do not require registration of customers' devices before the devices can initiate calls. Examples of such multimedia services include some VoIP services, promotional Web sites, anonymous multimedia chat services and customer service portals.
In contrast, other multimedia services may require registration before enabling the customers' devices to initiate calls to various callees. These multimedia services may allow unregistered devices a privilege of making some exception calls, which is defined as sessions/calls that are allowed to take place (and thus are not rejected) even if the required registration acts have not yet been carried out, but rejecting other outgoing calls. The exception calls may include emergency calls to 911 or 311. Exception calls may be allowed by either: modifying customer premises equipment (CPE) devices to simulate dial tones, modifying Internet Protocol Multimedia Subsystem (IMS) databases, introducing non-standard packets, using mobile technologies, or modifying an ENUM server.